Millimeter-wave signals increasingly find application in various fields and applications. In the telecommunications arena, for example, the United States has designated certain frequency bands in the millimeter-wave band for areas of future expansion. For example, the 38.6-40.0 GHz band has been chosen for licensed high-speed microwave data links, which experimental systems have shown capable of 10-Mbit/s over a microwave data link. Additionally, the 60 GHz band has been set aside for unlicensed short range data links providing data throughputs up to 2.5 Gbit/s. Many view the 60 GHz band as a solution to local loop bottlenecks in terrestrial metro and wide area networks. Indeed, an IEEE wireless standard dedicated to the 60 GHz range (802.11ad; “Very High Throughput 60 GHz”) is currently under development with the goal of encouraging the widespread adoption of 60 GHz wireless networks and related technologies. Furthermore, millimeter-wave signals find potential applications in outer space by way of highly-directional inter-satellite and extra-terrestrial communications. Still further applications for millimeter-wave signals exist in the medical industry, particularly in diagnostics and monitoring procedures such as non-invasive brain mapping, non-destructive in-situ testing.
New areas of application have also where millimeter-wave signals were previously thought to be ill-suited due to their perceived susceptibility to atmospheric attenuation. Specifically, certain low-attenuation windows in the millimeter-wave range (e.g., 35, 94, 140, and 220 GHz) have been found to be relatively immune from atmospheric attenuation. As a consequence, an entire host of additional applications for millimeter-wave signals in these windows is now likely, including target tracking and imaging, all-weather radiometry, and remote sensing.
Presently known oscillators for generating millimeter-wave signals, however, are ill-suited for several of these potential applications. Gunn diodes, although theorized for microwave through terahertz signal generation, are subject to severe tradeoffs between frequency and output power. Even in very mature material systems, Gunn diodes have not been realized in practice which offer sufficient power generation for most applications beyond the microwave regime for this very reason. In the case of the emerging families of wide bandgap compound semiconductor materials, the very doping levels which would be required for a Gunn diode to function also likely degrade electron velocity to the point of precluding Gunn oscillations in the first place. Moreover, travelling wave tubes, the devices most commonly used to generate millimeter waves at room temperature, have significant drawbacks including large size, high cost, and relative fragility. As a result, they too have significant shortcomings when it comes to implementing them in all of the potential applications available to millimeter-wave signals.
As a result, there remains a need for improved methods and systems for generating millimeter-wave oscillations. It is to this end that the methods and systems disclosed by the various embodiments of the present inventions are directed.